Add "go to last page" and page count to notifications and devices lists

The list endpoints now return a total count alongside the page so the
front-end can show how many pages exist and offer a last-page jump.

Backend: add count(is_new) and count_devices(...) (sharing a WHERE-builder
with list_devices so page and count can't drift), wrap both list responses
in {items, total_count} structs, and register them with utoipa.

Front-end: parse the wrapper shape (dropping the fetch-one-extra trick),
add a Last-page button and a responsive "Page X of Y" / "X / Y" label to
the shared PaginationBar, and track the total in both lists. Notifications
re-sync the count on every fetch and decrement it locally on mark-read/
unread removals so the count stays accurate without a re-fetch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/lib/widgets/pagination_bar.dart

@@ -1,23 +1,32 @@
 import 'package:flutter/material.dart';
 
+import '../theme/dimens.dart';
+
 class PaginationBar extends StatelessWidget {
   const PaginationBar({
     super.key,
     required this.currentPage,
-    required this.hasNextPage,
+    required this.totalPages,
     required this.isLoading,
     required this.onPageChanged,
   });
 
   final int currentPage;
-  final bool hasNextPage;
+  final int totalPages;
   final bool isLoading;
   final ValueChanged<int> onPageChanged;
 
   @override
   Widget build(BuildContext context) {
+    final lastPage = totalPages - 1;
     final canGoBack = currentPage > 0 && !isLoading;
-    final canGoForward = hasNextPage && !isLoading;
+    final canGoForward = currentPage < lastPage && !isLoading;
+    // Phones don't have room for the verbose label, so they get the compact
+    // "X / Y" form; wider layouts spell it out.
+    final isWide = MediaQuery.sizeOf(context).width >= Breakpoints.medium;
+    final label = isWide
+        ? 'Page ${currentPage + 1} of $totalPages'
+        : '${currentPage + 1} / $totalPages';
     // While a page change is in flight the buttons disable so the tap reads as
     // registered and double-taps are blocked; the progress cue itself is drawn
     // by the app shell at the bottom of the page body.
@@ -39,10 +48,7 @@ class PaginationBar extends StatelessWidget {
           ),
           Padding(
             padding: const EdgeInsets.symmetric(horizontal: 16),
-            child: Text(
-              'Page ${currentPage + 1}',
-              style: Theme.of(context).textTheme.bodyMedium,
-            ),
+            child: Text(label, style: Theme.of(context).textTheme.bodyMedium),
           ),
           IconButton.outlined(
             onPressed: canGoForward
@@ -51,6 +57,12 @@ class PaginationBar extends StatelessWidget {
             icon: const Icon(Icons.chevron_right),
             tooltip: 'Next page',
           ),
+          const SizedBox(width: 8),
+          IconButton.outlined(
+            onPressed: canGoForward ? () => onPageChanged(lastPage) : null,
+            icon: const Icon(Icons.last_page),
+            tooltip: 'Last page',
+          ),
         ],
       ),
     );